The trapping and collection of airborne contaminants in the form of gases, vapours, or the like is of importance in a number of fields. For example, contaminants may be collected to determine the downwind spread of herbicides or pesticides from a crop spraying operation to determine industrial compliance with air quality standards, to monitor the workplace air quality, or to control the use of toxic materials and to monitor and identify toxic substances released during military encounters.
The current techniques for collecting air samples are:
a. by using liquid filled impingers or bubblers. Air is drawn (bubbled) through the liquid which partially, or completely, dissolves the contaminants and thus removes them from the air stream. The solution is subsequently analysed by injection into, e.g., a gas chromatograph; PA0 b. by using tubes packed with a solid porous adsorbant. The solid material retains contaminants by, e.g., physical inclusion in pores or electrostatic attraction at active polar sites on the surface of the solid when air is drawn through the tubes. The solid material is subsequently solvent extracted and the extract is analysed, or the material is heated to thermally desorb the trapped contaminants into an appropriate apparatus for analysis; PA0 c. by collecting sample volumes of the air in suitable containers such as large bags or gas syringes. The air is withdrawn from the collection container using a small gas-tight syringe and injected into an analysis apparatus; PA0 d. by drawing air continuously through analysers which monitor contaminant concentration in real time or near real time.
The disadvantages of the prior art have been overcome as regards the sampling apparatus by, the system disclosed in the companion application referred to above, utilizing a cylindrical magazine containing a large number of mini-tubes prepacked with an absorbant material in which samples of the gas are collected. The object of this invention is to provide an automated desorption unit for removing the gas from the mini-tubes within a magazine and leaving the mini-tubes in a clean condition within the magazine ready for reuse in the sampling apparatus.